Over multiple generations, transistor devices (e.g., bulk, planar MOSFET devices) have been continually scaled down to smaller levels. However, the scaling of such devices has hit various roadblocks. For instance, as the source and drain regions of these devices are placed closer together, unwanted conduction may occur between the regions even when the device is turned off. This phenomenon is known as a short-channel effect.
To counter the drawbacks experienced by bulk, planar MOSFET devices, for instance, silicon-on-insulator (SOI) devices were developed SOI devices typically include a silicon substrate, a buried oxide formed on the surface of the silicon substrate, and a silicon body formed on the surface of the buried oxide. SOI devices typically show advantages over its bulk, planar MOSFET counterparts in various aspects (e.g., speed, power dissipation, latchup immunity, and reduction in process complexity and steps), particularly with short-channel-effect issues.
To further counter the drawbacks experienced by bulk, planar MOSFET devices, multi-gate devices have been introduced. Multi-gate devices typically prevent short-channel effects better than planar MOSFET devices, because multi-gate devices have greater control of the device's channel than planar MOSFET devices. In particular, a multi-gate device typically includes a non-planar channel that generally extends perpendicularly (or generally in the 112a direction as shown in FIG. 1) from the plane of the device (the plane of the device may extend in the 112b direction as shown in FIG. 1), and includes a gate that surrounds the channel on multiple sides rather than only on the top of the channel (as is the case with typical planar MOSFET devices).
The Fin-Field Effect Transistor (FinFET) device 100 is an example of such a non-planar SOI device. As shown in FIG. 1, the FinFET 100 may include a non-planar channel 106 with a gate 110 controlling the channel 106 from at least two sides, thus increasing gate control of the channel and potentially reducing short-channel effects. Further, the combination of a thin channel body and multiple gates significantly increase the mobility of the carriers in the channel.
Additionally, Inverted T Channel-Field Effect Transistor (ITFET) devices were introduced as an improvement over FinFET devices. As shown in FIG. 2, the ITFET 200 includes a non-planar channel 206 that includes a horizontal thin body 206a and vertical thin body 206b (or thin silicon region 206a and thick silicon region 206b). The horizontal thin body 206a increases the total available active region, thus providing more drive current per area in the ITFET device than typical FinFET devices. Further, the provision of the horizontal thin body 206a improves the mechanical stability of the channel 206, eliminates undercut of the buried oxide below the vertical thin body 206b, and reduces unwanted source/drain series resistances.
However, both FinFET and ITFET devices suffer drawbacks as well. For instance, in such non-planar SOI devices the channels 106 and 206 are typically left floating. When the channel of a non-planar SOI device is left floating, a floating body effect may be present. For instance, as the FinFET 100 is repeatedly turned on and off (ice, as a voltage is applied and reapplied to the gate 110), charge may accumulate in the channel 106.
This accumulated charge may cause any of a variety of adverse effects. For example, the accumulated charge may actually change the threshold voltage of the device. As another example, the accumulated charge may give rise to a history effect, meaning that the current state of the FinFET 100 at any given moment is dependent on the history of the device's biasing (i.e., dependent on how much charge has accumulated on the channel 106 as a result of the device's previous biasing).
Additionally, problems may arise from a charged particle collision (e.g., alpha particle) with the SOI device. If a charged particle collides with the channel 106, for instance, charge may accumulate in the channel 106. When the channel 106 is left floating, the charge may not (or take a relatively long time to) dissipate, and problems similar to that described above may occur.